1. Field of the Invention
The present invention relates to an electrical heating apparatus and more particularly to an electrical heating apparatus in which the electromagnetic fields and electrostatic fields associated with personal heating devices having positive temperature coefficient bodies are reduced to protect the user against health hazards associated with electromagnetic fields and electrostatic fields.
2. General Background
Electrically heated personal comfort, or medical aid, devices typically include an electrical resistance heating body threaded between a pair of fabric covers. Heat is generated and supplied to the user when electrical energy is applied across a heater wire which is woven with pockets or slots into which the resistance heating body is threaded. Conventionally, the temperature of the personal comfort device is controlled by a suitable controller connected to the resistance heating body.
An improvement to the personal comfort heating device is characterized by a heating portion of positive temperature coefficient, hereinafter termed PTC, material which is included in the resistance heating body. For examples of such devices see U.S. Pat. No. 3,410,984 issued to Sandford et al.; and, U.S. Pat. Nos. 4,271,350, 4,309,596 and 4,309,597 issued to Crowley.
However, the basic material from which the PTC heating portion is formed may be subject to conductor breakage. Sopory in U.S. Pat. No. 4,334,351 discloses extruding a second polymeric PTC material having great flexibility over an underlying PTC composition which is relatively rigid in order to prevent damage to the heating body from flexing, and, prevent conductor breakage. Ishii et al. discloses in U.S. Pat. No. 4,575,620 a heating portion having a positive temperature coefficient which is held in electrical contact with at least one of a first and second conductive bodies and a third conductive body acting as a fusing wire in the event of fracture of the PTC portion. Mills discloses in U.S. Pat. No. 4,577,094 a sensing wire and circuit to shut down a conventional blanket in the event of overheating. Thus, until the present invention, prior patents have been directed toward the personal safety of the user against an overheating failure which are commonly known to cause fires.
However, it has now been found that a more serious danger than that caused by overheating exists. Data as disclosed by D. Carpenter, "Report to the Fourth Annual EEPA Meeting", Bioelectromagnetics Society Newsletter, June 1988, and "Biological Effects of Power Line Fields" Panel's Final Report, New York State Power Lines Project, July 1987, which are incorporated herein, has been found to indicate that electromagnetic fields, and electrostatic fields contribute to tumor growth. Studies as disclosed by B. W. Wilson et al., "Domestic ELF Field Exposure and Peneal Gland Function", Tenth Annual Meeting Abstracts, BEMS, June 1988, which is incorporated herein, have definitely shown a correlation between malfunction of certain portions of the human endocrine system in the presence of conventional personal heating devices having positive temperature coefficient bodies. H. K. Florig et al. discloses in "Electric Field Exposure From Electric Blankets", IEEE Transactions on Power Delivery, April 1987, which is incorporated herein, that significant electric fields are present under electric blankets when heating.